Originally Posted by Cividasku
If you were on approach, in less than 30 seconds you end up with idle thrust and terrain warning to pull up.
Imagine they're in sync but you encounter a wiind gust, your speed reduces. The A/T will increase thrust, the trim will pitch down, both work to stabilize the airplane.
But if you're just 1kt off, the airplane will continuously want to enter an exponential dive to idle descent or climb to max power.
Eh? You're a pilot. Either YOU stay on the approach path/GS by pulling back on the stick, or let the AP coupled to the GS do it. This concept of letting the nose/flight path go up and down naturally because the actual speed is different to the TRS is nonsense. Something is (should be!) actively controlling the pitch attitude and therefore flight path so you won't end up diving into the ground at Idle power.
My last jet, the 717, was a classic example of this. Slack glidepath control, allowing the nose to wander, resulted in the ATS staying up when it should have ben coming back, and staying back when it should have been coming up. However, with tight slope control eg if you get hit on the face with a gust and you balloon, you stay on the slope with a push (ie don't let the nose come up) and the instant you start to apply forward pressure the ATS says OK! and pulls the power off. The speed then comes back to the TRS/bug speed. But all the while, I have
actively stayed on the desired approach slope.
I always used the ATS. It was a fantastic system in the 717.
Jets should/can't be flown like Pipers on final. You don't pull the power off to make the jet down down by relying on the secondary effects of controls. You push the nose down, then adjust the power
if you need to (or let the ATS do it for you).
You're obviously an FO: "Always remember and forever take heed, right hand for glidepath and left hand for speed!". Or, if you have an ATS, it can do the left-hand bit for you.